1. Field of the Invention
The present invention relates to an ink depletion detection apparatus for detecting the empty state of ink in an ink reservation container or the like of an ink jet recording apparatus or a residual quantity detection apparatus for detecting the residual quantity of ink in the same.
More particularly, the present invention relates to an ink residual quantity detection apparatus for detecting the quantity of residual ink accommodated in an ink reservation container consisting of a plurality of accommodating members capable of accommodating different inks in different states.
2. Related Background Art
A recording apparatus having functions to serve as a printer, a copying machine and a facsimile machine or a recording apparatus for use as an output unit for a combined electronic apparatuses including a computer, a word processor and the like has a structure capable of recording an image on a recording medium, such as paper or a thin plastic plate, in accordance with image information. The recording apparatuses are classified into ink jet recording apparatuses, wire dot recording apparatuses, thermal recording apparatuses and laser beam recording apparatuses in terms of the recording method.
The recording apparatus employing the ink jet recording method (the ink jet recording apparatus) records an image by discharging ink from a recording means (a recording head) to a recording medium. The ink jet recording apparatus have a variety of advantages in that the size of the recording means can be reduced, a precise image can be recorded at high speed, an image can be recorded on plain paper without special treatments, the running cost can be reduced, noise can be prevented because the non-impact recording method is employed, and a color image can easily be recorded by using a multiplicity of color inks.
In particular, the ink jet recording means, which uses thermal energy to discharge ink, can easily be manufactured into a form that comprises a means having dense liquid passage arrangement (configuration of discharge ports) by performing the semiconductor manufacturing process, which includes etching, evaporation and sputtering, to form an electricity-to-heat converter on the substrate, electrodes, liquid passage walls, ceiling plate and the like. Thus, the size of the recording means can be reduced further satisfactorily.
The ink jet recording apparatus has an ink reservation unit for reserving ink to be supplied to the recording head, the ink reservation unit being mounted fixedly on a predetermined position in the ink jet recording apparatus or mounted on the carriage together with the recording head. In the former case, an ink supply passage, such as an ink tube, is formed between the recording head and the ink reservation unit in such a manner that the ink supply passage is able to follow the movement of the carriage. In the latter case, the ink supply passage between the recording head and the ink reservation unit can relatively be shortened. Accordingly, the foregoing structure, in which the ink reservation unit is mounted on the carriage, is suitable to reduce the size of the ink jet recording apparatus and simplify the structure of the same.
The foregoing structure, in which both recording head and the ink reservation unit (ink tank) are mounted on the carriage, in the category thereof, includes a structure, in which both recording head and the ink tank are integrally formed, and a structure in which the recording head and the ink tank are separately mounted.
With the structure, in which the recording head and the ink tank are integrally formed, a cartridge having the ink tank and the recording head formed integrally is changed to a new cartridge when ink in the ink tank has been consumed. Cartridges of the foregoing type have been used widely in recent years because they can easily be handled. However, the running cost cannot be reduced because the costly head must be changed whenever ink has been consumed.
With the latter structure having the recording head and the ink tank which are mounted separately, only the ink tank reserving ink is changed when the ink has been consumed but the head is required to be changed only after its lifetime.
If the recording head is used in a usual manner, use of the recording head is not inhibited during its lifetime before ink in the ink tank is used completely. Therefore, the recording head must be changed by the number of times which is smaller than the number of times required for the ink tank to be changed. Since only the relatively low cost ink tank is usually changed, the running cost can be reduced. However, the foregoing structure comprising the recording head and the ink tank, which are mounted separately, requires the portion for establishing the connection between the ink tank and the recording head to be manufactured-precisely in order to prevent ink leakage.
The recording apparatus adapted to the ink jet recording method must be capable of satisfactorily supplying ink in a quantity to be discharged through the recording head during the recording operation, and as well as must have an ink supply system capable of preventing ink leakage through the discharge port in a period in which the recording operation is not performed.
The foregoing problem of ink leakage through the discharge port is a peculiar problem for the ink jet recording apparatus. In order to overcome the foregoing problem, the pressure at the discharge port has been usually lowered as compared with the atmospheric pressure. To realize the foregoing state of pressure, the ink jet recording apparatus has a negative pressure generating mechanism provided for the ink supply system thereof. Note that the "negative pressure" is back pressure with respect to the direction, in which ink is supplied to the discharge port, and a state of pressure, in which the pressure at the discharge port is lowered than the atmospheric pressure, is meant.
If the ink accommodating portion is in the interchangeable form, there arise necessities that the ink accommodating portion can be attached/detached smoothly without ink leakage so as to reliably supply ink to the recording head, in addition to the foregoing requirements.
An example of the structure of the ink container serving as the ink accommodating portion for use in the ink jet recording apparatus has been disclosed in Japanese Patent Laid-Open No. 63-87242 (hereinafter called a first conventional example). According to the first conventional example, a structure of an ink jet recording carriage has been disclosed which comprises an ink container substantially completely filled with a foaming material and a plurality of ink discharge orifices.
In the ink container of the foregoing type, negative pressure can be generated due to the capillary force of a porous medium, such as polyurethane foam which is the foaming material for reserving ink and ink can be held (ink leakage from the ink container can be prevented).
However, the foregoing first conventional example requires the foaming material to be substantially completely enclosed in the ink accommodating portion, whereby limiting the quantity of chargeable ink. Furthermore, the quantity of residual ink in the foaming material is large as compared with the ink container accommodating only ink. Thus, there arises a problem in that the efficiency in use of the ink is unsatisfactory.
In order to enlarge the quantity of chargeable ink in the structure comprising a foaming material to serve as the negative pressure generating means in the ink reservation means, a structure has been disclosed in Japanese Patent Laid-Open No. 6-40043. According to the foregoing disclosure, an ink reservation container comprising a portion for accommodating a negative pressure generating member and an ink accommodating portion for accommodating ink, which are divided from each other, is employed so that ink except a portion, which adheres to the wall of the ink accommodating portion, can substantially completed be used. Thus, the capacity of the ink reservation container can be enlarged. Furthermore, the accommodated negative pressure generating member prevents ink leakage from the recording head so that the performance of supplying ink is stably maintained for a long time.
In any type of the foregoing ink jet recording apparatuses, it is preferable that the ink reservation means be changed at appropriate timing. Furthermore, there is a necessity of providing a means for accurately detecting the quantity of ink left in the ink reservation means and a means for appropriately detecting the moment at which ink will be consumed.
If ink in the ink reservation means is empty, the discharge means for discharging ink through the recording head generates the discharge energy in the state where the ink reservation means does not accommodate ink. In particular, a so-called bubble jet ink recording apparatus, which comprises a thermal energy generating means, such as an electricity-to-heat conversion device, as a discharge means to use pressure generated due to status change caused by the heat of ink so as to discharge ink, encounters undesirable rise in the temperature of the recording head and damage of the recording head if the thermal energy generating means is operated in the state where no ink is left.
In an ink jet recording apparatus comprising a mechanical pressure generating means, such as a piezoelectric device, to serve as a discharge means for discharging ink, operation of the discharge means in a state where no ink is left causes the mechanical pressure generating means to continuously generate pressure without load acting during the ink discharge. As a result, the discharge means and durability deteriorate.
Hitherto, there have been disclosed a structure for detecting ink empty state (state where ink has been consumed) in the ink reservation container for an ink jet recording apparatus as in Japanese Patent Laid-Open No. 54-133733 which comprises an optical device for detecting the light transmission state in an ink tank, as in Japanese Patent Publication No. 1-17465 in which the empty state is detected by electrically conducting an electrode member, and as in Japanese Patent Laid-Open No. 59-194853 in which the number of discharge pulses is counted to estimate the quantity of consumed ink (hereinafter called a "dot counter method").
However, the foregoing conventional ink empty state detection apparatus (the ink residual quantity detection apparatus) cannot accurately detect the residual quantity of ink when adapted to the structure in which a foaming material serving as the negative pressure generating member is enclosed in the ink reservation means or the structure of the ink reservation container in which the portion for accommodating the negative pressure generating member and the ink accommodating portion are separated from each other.
Among the conventional structures, the structure for detecting the light transmission state of the ink tank by using an optical device and the structure for detecting the empty state by detecting an electrode member encounters difficulty in detecting ink empty in the ink tank accommodating the negative pressure generating member because of the structure of the ink reservation container. Even if the residual quantity of ink left in only the ink accommodating portion of the structure, in which the portion for accommodating the negative pressure generating member and the ink accommodating portion are separated from each other, is detected, a considerably large quantity of ink is left in the portion for accommodating the negative pressure generating member whereby allowing the foregoing structure to be used only to alarm somewhat reduction in the quantity of ink.
The structure for detecting the residual quantity by electrically conducting an electrode member sometimes encounters adverse influence upon ink supply if a desired negative pressure cannot be realized in a case where the disposed electrode compresses the negative pressure generating member.
The dot counter method cannot prevent an error because the quantity of use becomes different depending upon scattering in the quantity of discharge per one discharge operation, scattering in the quantity of ink initially charged into the ink tank and the difference in the quantity of use due to the environment for use. The foregoing error is sometimes the half of the overall quantity of ink, thus resulting in that issue of an alarm indicating reduction in the residual quantity or interruption of the operation of the recording apparatus must be performed in a state where substantially the half quantity of ink is left in order to reliably perform the same. If the alarm or interruption is performed at a timing at which a considerably large quantity of ink is left, the purpose of detecting the residual quantity cannot be achieved or ink will be used wastefully. If the residual quantity is detected accurately by the dot count method, the cost cannot be reduced. Since the capacity of the ink reservation container has been enlarged recently, the residual quantity of ink cannot accurately be detected.
In view of the foregoing, the present invention employs a structure for detecting reflected light of light made incident upon the ink tank. However, the structure for detecting reflected light has the following problems to be overcome.
As a sensor for emitting light and detecting reflected light, a photointerrupter is usually employed in which an LED serving as a light emission means and a phototransistor serving as a light receiving means are accommodated in one package. Since the lifetime of a photointerrupter is usually shorter than that of a printer, the LED is turned on only when it is used to shorten the time, in which electric power is supplied to the photointerrupter.
Since both light emission quantity of the LED and the sensitivity of the phototransistor of a photointerrupter scatter, the combined photocurrent output characteristic of the LED and the phototransistor scatters by about two times to four times between the upper limit and the lower limit. In a case where the photointerrupter is used to serve as the ink empty detection apparatus, the output from the photointerrupter must be adjusted to be included in a predetermined range, that is, so called calibration must be performed.
The calibration is performed by, for example, in such a manner that a reflecting portion for calibration having a predetermined reflectance is provided, the reflecting portion is irradiated with light emitted from an LED, light reflected by the reflecting portion is detected by a phototransistor, and a variable resistor for limiting the LED current is so adjusted that the output from the phototransistor is included in a predetermined range.
However, the foregoing calibration operation has a plurality of problems.
For example, the operation for calibrating the output from a photointerrupter 6 by adjusting a variable resistor 87 for limiting the LED current cannot easily be automated, whereby increasing the manufacturing processes.
If an excessive error takes place in adjusting the output from the photointerrupter during the foregoing operation, there is a risk of erroneous result in detecting ink depletion. Accordingly, accurate adjustment must be performed, whereby further increasing the manufacturing labor.
Since the foregoing operation is performed in a process for adjusting the printer to be performed in a manufacturing plant, change in the quantity of light emitted from the LED 5 occurring due to time lapse or change in the output from the photointerrupter 6 occurring due to contamination of the same after the printer has been shipped changes the output from the photointerrupter 6. Thus, depletion of ink cannot accurately be detected.
The structure using the photointerrupter to detect the residual quantity of ink in the ink tank has problems to be overcome to detect it further accurately. The reason for this is that the ink residual quantity detection apparatus that irradiates the ink tank with light and measures the difference in the quantity of reflected light to discriminate empty of ink has the following problem: LEDs for emitting light must emit light in the same quantity (the LEDs generally emit light in different quantities). Therefore, the quantities of light emitted from LEDs must be measured to select an LED determined to emit light in a quantity included in a predetermined range. The reason for this is that the difference in the quantity of light emitted by the LED causes the quantity of light received by the light receiving device to be different. Furthermore, the foregoing difference affects the change in the output from the light receiving device, with which the ink empty is discriminated. A similar phenomenon applies to the light receiving device. Thus, the output value must be constant with respect to the quantity of received light. Therefore, the light receiving device must receive light in a predetermined quantity and have a constant output characteristic. The foregoing necessity of selecting a light emitting device and light receiving device enlarges the cost.
In addition to the requirements for the devices, the system for operating the photointerrupter must be subjected to an error adjustment process. In the foregoing system, there are involved the voltage level for operating the LED portion of the photointerrupter, allowable manufacturing error in the value of the current limiting resistor for limiting the electric current that flows in the LED, allowable error in the current-to-voltage conversion resistor in the light receiving portion and conversion error occurring in an AD convertor. The foregoing errors must be adjusted for each ink jet printer. It leads to a fact that the adjustment operation to be performed in the manufacturing plant increases and thus the cost of the printer is enlarged.
Since the conventional ink jet recording apparatus has the structure that the distance from recording paper to the recording head is changed to correspond to the thickness of the recording paper, there arises a problem in that the change in the distance from the recording paper to the recording head must be considered when the sensitivity of the photointerrupter is corrected.
A printer, which has a plurality of detection mechanisms, such as a mechanism for detecting the distance from the carriage to the paper, in addition to the mechanism for detecting the residual quantity of ink, inevitably has a complicated internal structure, and the overall cost of the printer cannot be reduced. In particular, a printer having a simple structure cannot easily be provided with a plurality of detection mechanisms of the foregoing type. However, sensors serving as the foregoing detection mechanism are required to prevent defective recording operation or a critical failure for the printer. Accordingly, a low cost sensor apparatus has been required.